The present invention relates to surgical clips and clip appliers and more particularly to penetrating polymeric hemostatic clips and instruments for applying them.
Surgical clips like hemostatic clips and aneurysm clips are often used in surgery to ligate vessels to stop the flow of blood. Surgical clips are also used to interrupt or occlude the oviduct or vas deferens in sterilization procedures. The clips are left in place permanently and within a period of time the ligated end of the vessel will close, that is, hemostasis or occlusion will occur.
Metal clips having generally U or V shapes have been used for years. The most common metals are alloys of tantalum, titanium or stainless steel, all of which are deformed into a closed position about the vessel and because of the nature of the metal stay deformed and resist any force by the vessel to expand or open up.
Metal clips cause a certain amount of interference with high technology diagnostic modalities, including Computer Tomography (CATSCAN) and Magnetic Resonance Imaging (MRI). In particular, the new and emerging MRI techniques place stringent demands on the non-interference properties of clips. For example, existing fast imaging techniques for MRI give rise to at least one order of magnitude in increased sensitivity to magnetic field inhomogenieties brought about by metallic clips. Field uniformities of one in 10.sup.5 are required but metal clips, particularly stainless steel clips, can reduce the homogeniety in the locality of the clip to the order of 10.sup.4 or less.
To aggravate the situation even more recent developments in in vivo Magnetic Resonance Spectroscopy (MRS) create even greater demands on minimizing magnetic field interferences (field uniformities approximately one in 10.sup.7 required). Existing metal clips preclude the use of MRS data taken in the proximity of the metal clips. This region is as large as six clip diameters for titanium and tantalum and more than fifty clip diameters for stainless steel.
To overcome the above problems, in recent years plastic clips have been introduced. These clips generally should be as small as possible, e.g., as small as their metal counterparts. Plastic clips require a latching means to keep the clip closed once they are clamped about the vessel since, unlike metal clips, they have insufficient resistance to the forces tending to open the vessels. The requirement to latch presents an additional problem since the polymeric clip must surround the vessel to do so. Therefore, the vessel to be ligated must not be attached to any surrounding tissue. Without more, such clips would require that the surgeon dissect the vessels from the surrounding connective tissue and this would be very time consuming. With metal clips this is not necessary since metal clips need not surround the vessel to occlude it. It is desirable, therefore, to provide a polymeric clip capable of occluding a vessel attached to connective tissue.
Most of the new plastic clips now in the market are made of a biodegradable and absorbable polymeric material. Generally, the absorbable clips, owing to their comparatively high water sorption do not reflect the mechanical strength levels which are available from modern engineering plastics and therefore represent a size increase compromise in order to provide comparative strength. The use of high performance polymer materials permits increased design options for functional improvements.
It is, therefore, desirable to produce a small, but secure, biocompatible and strong polymeric surgical clip which may be used to close vessels connected to surrounding tissue.